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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: State-of-the-art theoretical and numerical techniques required to simulate the head-disk interface (HDI) of future magnetic storage devices is presented. The severity of operating conditions (i.e., attempts to achieve flying heights as low as 40 nm) pose several challenges. Large transient pressure gradients can be established within air bearing leading to numerical oscillations as well as to increased program execution times. Enhanced gaseous rarefaction effects must also be incorporated into the analysis. In the present study, accurate nonoscillatory air bearing pressure distributions were obtained using a high resolution finite element algorithm to solve the generalized Reynolds equation. Higher order gaseous rarefaction effects are incorporated into generalized Reynolds equations using the total mass flow rate coefficient predicted from the linearized Boltzmann equation. The form of the generalized Reynolds equation that is presented in this paper is an improved version of the continued fraction approximation previously proposed by Crone et al.1 A simple scaling analysis, which is based upon the results of the linearized Boltzmann equation, will also be presented to study the effect of slider miniaturization, as well as to obtain a novel interpretation of accelerated wear and accelerated flyability test results.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2440-2444 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fano's tetradic representation of Liouville–Neumann operators is used as the basis of a systematic procedure for solving an important class of rheological equations of state. This procedure is complementary to the techniques which Bird and his co-workers have used in their studies of complicated rheological models. To illustrate how our method works it is applied to a rheological model of the Maxwell–Oldroyd type. Explicit formulas are derived for the stress tensors associated with a number of time-independent, homogeneous flows.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 3972-3977 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An off-lattice Monte Carlo simulation using a coarse-grained bead-spring model was developed to analyze nanoconfined polymer films. The beads in the polymer chains are connected via finitely extensible, nonlinear elastic springs. In addition to nonpolar van der Waals interactions, functional endbeads have a short-range exponential interaction characteristic of endgroup coupling. Our simulated results qualitatively agree with experimental data for perfluoropolyether molecules with functional endgroups in ultrathin films. The chains exhibit an oblate conformation near the wall, but recover a spherical shape as they move farther away from it. The density profile of functional endbeads as a function of distance from the wall shows characteristic oscillation originating from endbead coupling and orientation near the wall. We examined the molecular layering of films via the analysis of an anisotropic radius of gyration for the chains, which is affected by the endgroup interactions. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 1026-1034 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9613
    Keywords: Projection operator ; mode-mode coupling ; non-Hamiltonian method ; chemical reaction ; bimolecular reaction ; hydrodynamicmode ; reactive mode ; diffusion-controlled reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of the coupling between chemical reaction and diffusion in a dense fluid. Our analysis utilizes the projection operator formalism and a generalized Langevin equation that is based on irreversible, phenomenological equations of motion instead of conventional Hamiltonian mechanics. It also is shown that this same “non-Hamiltonian” theory provides a simple way of deriving Kawasaki's mode-mode coupling theory of diffusion.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9613
    Keywords: Particulate filler ; composites ; Green's function ; Oseen tensor ; elastic interaction tensor ; suspension rheology ; Lamé constant ; effective medium theory ; elastic screening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe a new, effective medium theory to study the wave propagation and mechanical properties of a composite system with dispersed particulates. One main emphasis here is in formulating the theory and in analyzing the structure of the contribution of the fillers to the elastic response. By constructing the elastic propagator (whose fluid mechanical counterpart is known as the Oseen tensor), we show that an analogy between the theoretical description of the particulate system and of suspension rheology exists when the former corresponds to a high-rigidity solid matrix (or, analogously, when the Poisson ratio is close to 1/2) in steady state. The effective Lamé constants for this case are derived by combining this analogy with the theory developed by Freed and Muthukumar for the rheology of a suspension of spheres. The analogy is also useful in our new prediction of the phenomenon of elastic screening, the possible existence of a cutoff frequency below which elastic waves cannot propagate in the filler system.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effects of temperature, molecular weight and its distribution, side chain branching, and the structure of polymers on the elastic behavior of bulk homopolymers were investigated, by using logarithmic plots of first normal stress difference (N1) against shear stress (σ12) and logarithmic plots of storage modulus (G′) against loss modulus (G″). For the investigation, we have used data from the literature as well as our recent experimental results, covering a very wide range of temperature and shear stress or loss modulus. It has been found that such plots are very weakly sensitive to (or virtually independent of) temperature and to the molecular weight of high molecular weight polymers, but strongly dependent upon the molecular weight distribution and the degree of side chain branching. A theoretical interpretation of the observed correlations is presented, using molecular theories.
    Additional Material: 31 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Flow-induced polymer migration is treated in a rather intuitive though mathematically formal way. It is important to incorporate hydrodynamic interaction effects as well as flow geometry effects in studying polymer migration perpendicular to the flow direction. Simple examples, circular Couette flow in the free-draining limit and plane Poiseuille flow in the nondraining limit, are chosen to illustrate the importance of such effects.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The theory of Freed and Edwards is used to investigate polymer migration in nonhomogeneous flow fields with confined geometry. Polymer migration from the main flow originates in three effects: (i) nonhomogeneous flow-field effect, (ii) the confined-geometry effect, and (iii) the concentration effect. General correlation function formulas for these three effects are explicitly derived. Some specific examples are illustrated and solved by using the harmonic dumbbell and Rouse-Zimm models.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We study the effect of the memory function on the coherent scattering function of a dilute polymer solution, taking into account hydrodynamic interactions among the polymer segments. The line shape, given by a sum of two exponentials, is very accurate numerically for ka ≳ 3 (with a the length of a polymer segment) and for times such that ω0(k)t ≲ 1.5 [with ω0(k) the initial slope]. However, this approximation to the scattering function is not nearly so accurate at the smaller values of ka encountered in light scattering experiments. The amplitudes and relaxation times associated with the two exponentials are found to be markedly dependent on the strength of the hydrodynamic interactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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